1. Field of the Invention
This invention relates generally to the subconscious parafunctional mandibular habits known as bruxism or clenching and more particularly an interocclusal appliance for the prevention of tooth structure loss resulting therefrom.
2. Antecedents of the Invention
Various studies have been undertaken with respect to the causative factors and precise mechanisms involved in bruxism and clenching. For example, it has been found and that bruxing events could be categorized based on mandibular position patterns.
Studies have also demonstrated that the highest amplitude of nocturnal bite force during bruxism could exceed the amplitude of the maximum voluntary bite force during the daytime. Bruxism and clenching have been found to constitute a major factor in conjunction with occlusal surface wear and constitute a significant potential risk factor for implant failure.
Interocclusal appliances, such as nightguards, have been long recognized as beneficial for the alleviation of the adverse effects of bruxism and clenching.
Prior interocclusal appliances included those fitted by a dental professional and those which were self fitted. Professionally fitted interocclusal appliances were molded of relatively hard acrylic resin from casts of the patient""s mouth taken from a dental impression. This procedure was both time consuming and expensive.
A typical self fitted interocclusal appliance included a thermoplastic channel trough in the configuration of a maxillary arch. Carried in the trough was a thermoplastic impressionable liner material having a softening point temperature lower than that of the trough. The liner was molded to conform to the mouth of the user after the appliance was immersed in hot water and then inserted into the mouth, with the liner placed against the maxillary arch. The user""s jaw was then closed and biting pressure was applied to force the maxillary teeth into the liner.
Problems which were encountered with respect to self fitting nightguards included those related to the fitting procedure itself and to the durability of the appliance. The inability to properly center and align, i.e. register, the heated impressionable liner material of the nightguard relative to one""s own maxillary arch constituted a major deficiency. When the nightguard was not properly registered, an improper fit was obtained, resulting in discomfort as well as premature appliance wear.
Further problems were encountered with respect to the structural integrity of self fitting nightguards. As a result of the shear forces which were generated during bruxing or clenching events, separation of the bond between the liner and the trough occurred. With the trough in contact with the mandibular occlusal surfaces and the maxillary teeth embedded in the liner, lateral, superior and anterior mandibular deviations during bruxing events resulted in shear stress which separated the liner from the trough, rendering the appliance unserviceable.
A self fitting interocclusal appliance includes a base having a generally planar, smooth, occlusal face and a pair of parallel curved side walls. The base is molded of a thermoplastic having a Vicat softening temperature of at least 65xc2x0 C. and a Shore A hardness of at least 80.
Molded into the base between and above the side walls is an impression preform comprising an EVA copolymer having approximately thirty percent vinyl acetate, a Vicat softening temperature of approximately 36xc2x0 C. and a Shore A hardness below 80.
The preform includes a thick footing having a planar upper face and a shallow bight shaped centric relation pilot channel defined by peripheral walls which are sloped downwardly and inwardly from an elevation above the side walls of the base. The upper face of the footing defines the bottom of the pilot channel.
The base and preform are bonded to form a unitary appliance which is fitted by immersion in hot water such that the preform copolymer reaches a temperature above its softening temperature yet which can be comfortably withstood by oral tissue. The appliance is thereafter inserted in the oral cavity with the centric relation pilot channel substantially registered with the teeth of the maxillary arch. Light pressure is applied to seat the maxillary occlusal surfaces in the shallow preform pilot channel, after which biting pressure is applied to imbed the maxillary teeth in the preform footing.
Since the softening temperature of the base thermoplastic was not attained during the heating step, significant deformation of the base is avoided and the upper and lower occlusal surfaces are separated by at least the thickness of the base.
Upon cooling to oral cavity temperature, the preform is transformed into a reusable resilient flexible encasement for the maxillary dentition (maxillary encasement), with the appliance to be removed during day time hours and reused at bed time.
Suitable thermoplastics for employment as the preform include ELVAX(copyright) EVA copolymer and suitable thermoplastics for employment as the base include ELVALOY(copyright) EMA copolymer, ELVALOY(copyright) EMA blended with ELVAX(copyright) EVA or ELVALOY(copyright) EMA blended with PELLETHANE(copyright) TPU elastomer.
From the foregoing compendium, it will be appreciated that it is an aspect of the present invention to provide an interocclusal appliance of the general character described which is not subject to the disadvantages of the antecedents of the invention aforementioned.
A feature of the present invention is to provide an interocclusal appliance of the general character described which is particularly well adapted for self fitting.
It is a consideration of the present invention to provide an interocclusal appliance of the general character described which is well-suited for economical mass production fabrication.
Another aspect of the present invention is to provide an interocclusal appliance of the general character described which is configured for accurate centric relation self fitting.
A further feature of the present invention is to provide an interocclusal appliance of the general character described which reduces stresses imposed on tooth surfaces during bruxing events.
Another consideration of the present invention is to provide an interocclusal appliance of the general character described which is safe and easy to use.
Yet another aspect of the present invention is to provide an interocclusal appliance of the general character described suited for extended usage without deterioration.
To provide an interocclusal appliance of the general character described having a base and an impression material unitarily molded thereto and characterized by a high shear resistance bond between components is a still further consideration of the present invention.
Another feature of the present invention is to provide an interocclusal appliance of the general character described which prevents loss of tooth structure otherwise resulting from bruxing events.
Another aspect of the present invention is to provide an interocclusal appliance of the general character described which is uninhibiting and comfortable to wear.
To provide an interocclusal appliance of the general character described which reduces compressive and lateral forces upon individual tooth surfaces occurring during bruxing events is a still further consideration of the present invention.
A further feature of the present invention is to provide an interocclusal appliance of the general character described which promotes restful sleep.
Further aspects, features and considerations of the present invention in part will be obvious and in part will be pointed out hereinafter.
With these ends in view, the invention finds embodiment in the various combinations of elements, arrangements of parts and series of steps by which the aforesaid aspects, features and considerations and certain other aspects, features and considerations are attained, all with reference to the accompanying drawings and the scope of which will be more particularly pointed out and indicated in the appended claims.